Drilling fluids used in the drilling of subterranean oil and gas wells along with other drilling fluid applications and drilling procedures are well known. In rotary drilling there are a variety of functions and characteristics that are expected of drilling fluids, also known as drilling muds, or simply “muds”. The functions of a drilling fluid include, but are not necessarily limited to, cooling and lubricating the bit, lubricating the drill pipe and other downhole equipment, carrying the cuttings and other materials from the hole to the surface, and exerting a hydrostatic pressure against the borehole wall to prevent the flow of fluids from the surrounding formation into the borehole.
Drilling fluids are typically classified according to their base fluid. In water-based muds, solid particles are suspended in water or brine. Oil can be emulsified in the water which is the continuous phase. Brine-based drilling fluids, of course are a water-based mud (WBM) in which the aqueous component is brine. Oil-based muds (OBM) are the opposite or inverse. Solid particles are suspended in oil, and water or brine is emulsified in the oil and therefore the oil is the continuous phase. Oil-based muds can be either all-oil based or water-in-oil macroemulsions, which are also called invert emulsions. In oil-based mud, the oil may consist of any oil that may include, but is not limited to, diesel, mineral oil, esters, or alpha-olefins.
The use of asphalt and derivatized asphalt in both oil-based and water-based drilling fluids is well established. Asphalt is used in drilling fluids to improve filtration control, improve lost circulation control, prevent drill string differential sticking, to stabilize the wellbore, and/or to control seepage loss into laminated or microfractured shale by means of bridging and sealing the microfractures at the wellbore interface. Although asphalt can be used in oil-based drilling fluids without modification, it is necessary to change the wetting and dispersing properties of asphalt in order to make the material dispersible and somewhat soluble in aqueous fluids. Two common approaches to improve the water dispersibility/solubility of asphalt are 1) surfactant addition and 2) sulfonation. Both types of modified asphalt are currently used in water-based drilling fluids. As used herein, asphaltite refers to any of various bitumens containing asphaltenes.
It would be desirable if compositions and methods could be devised to aid and improve the introduction of asphalts into drilling fluids beyond the techniques already known to give more choices to drilling operators.